The present invention relates, in general, to electronics and, more particularly, to semiconductor device structures and methods of forming semiconductor devices.
Power semiconductor devices, such as rectifiers, thyristors, bipolar transistors, metal oxide semiconductor field effect transistors (MOSFETs) are used in a wide variety of power conversion system. Such devices can be configured to control the flow of current through ON/OFF switching operations. The efficiency of a power conversion system may depend on the efficiency of the power semiconductor devices used in the power conversion systems.
Many power semiconductor devices used in power conversion systems are based on silicon. However, due to certain physical limitations of silicon and associated manufacturing processes used to make silicon-based devices have made it difficult to further increase the efficiency of silicon-based power semiconductor devices for certain applications. For example, some silicon-based devices use thick regions of lightly doped or intrinsically doped material that support high breakdown voltages, but result in high voltage drops in forward conduction mode. In high current applications, this is one source of power losses. Also, higher voltage silicon-based devices tend to have longer reverse recovery times, which further impact the efficiency of these devices. Additionally, discrete power semiconductor devices are often co-packaged with other electronic devices, which have made assembly and packing processes more complex, and this approach has generated parasitics into the power conversion system. Such parasitics have impaired system performance.
Accordingly, improved power semiconductor structures and methods of integrating and/or making such structures are needed that address the issues described above including power loss reduction as well as others. It would be beneficial for such structures and methods to be cost effective and compatible for manufacturing integration, and to not detrimentally affect device performance.
For simplicity and clarity of the illustration, elements in the figures are not necessarily drawn to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein, current-carrying electrode means an element of a device that carries current through the device, such as a source or a drain of an MOS transistor, an emitter or a collector of a bipolar transistor, or a cathode or anode of a diode, and a control electrode means an element of the device that controls current through the device, such as a gate of a MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain N type regions and certain P type regions, a person of ordinary skill in the art understands that the conductivity types can be reversed and are also possible in accordance with the present description. Also, the devices explained herein can be Ga-face GaN devices or N-face GaN devices. One of ordinary skill in the art understands that the conductivity type refers to the mechanism through which conduction occurs such as through conduction of holes or electrons, therefore, and that conductivity type does not refer to the doping concentration but the doping type, such as P type or N type. It will be appreciated by those skilled in the art that the words during, while, and when as used herein relating to circuit operation are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay(s), such as various propagation delays, between the reaction that is initiated by the initial action. Additionally, the term while means that a certain action occurs at least within some portion of a duration of the initiating action. The use of the word approximately or substantially means that a value of an element has a parameter that is expected to be close to a stated value or position. However, as is well known in the art there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to at least ten percent (10%) (and up to twenty percent (20%) for semiconductor doping concentrations) are reasonable variances from the ideal goal of exactly as described. The terms first, second, third and the like in the claims or/and in the Detailed Description of the Drawings, as used in a portion of a name of an element are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments described herein are capable of operation in other sequences than described or illustrated herein. For clarity of the drawings, doped regions of device structures are illustrated as having generally straight line edges and precise angular corners. However, those skilled in the art understand that due to the diffusion and activation of dopants the edges of doped regions generally may not be straight lines and the corners may not be precise angles. Additionally, it is to be understood that where it is stated herein that one layer or region is formed on or disposed on a second layer or another region, the first layer may be formed or disposed directly on the second layer or there may be intervening layers between the first layer and the second layer. Further, as used herein, the term formed on is used with the same meaning as located on or disposed on and is not meant to be limiting regarding any particular fabrication process. Moreover, the term “major surface” when used in conjunction with a semiconductor region, wafer, or substrate means the surface of the semiconductor region, wafer, or substrate that forms an interface with another material, such as a dielectric, an insulator, a conductor, or a polycrystalline semiconductor. The major surface can have a topography that changes in the x, y and z directions.